1. Field of the Invention
The present invention relates to a passive entry system for a motor vehicle having a remote keyless access device and interior and exterior vehicle antenna for use in detecting a location of the remote keyless access device.
2. Background
It is well known in the automotive industry to provide for remote vehicle access, such as through the use of remote keyless entry (RKE) systems. Such RKE systems use a remote hand held transmitter, which is commonly referred to as a “fob.” Currently available RKE fobs may be separate units, or may be part of an ignition key head. Such RKE fobs generally transmit radio frequency (RF) signals to a vehicle in order to lock or unlock vehicle doors, open or close a vehicle sliding door, unlock a vehicle trunk, activate internal and/or external vehicle lights, activate a “panic” alarm, and/or perform a variety of other functions.
In that regard, such RKE systems also typically include a receiver and/or control unit installed in the vehicle. The receiver and/or control unit may be provided in communication with door locking mechanisms to lock and unlock the vehicle doors in response to lock or unlock signals received from the remote transmitter within some pre-defined range. Similarly, the receiver and/or control unit may be provided in communication with other vehicle devices to control operation thereof in response to other signals received from the remote transmitter.
The RKE systems of the types described above may be characterized as active in nature, where a switch or pushbutton on the remote transmitter must be activated by an operator in order to have a desired remote access function performed, such as locking or unlocking the vehicle doors. Alternatively, RKE systems may also be passive in nature, where no such switch or pushbutton activation by an operator is required in order to perform a desired remote access function.
In that regard, in a passive keyless entry system, a remote transceiver, which may be referred to as a “fob” or a “card,” is typically provided for communicating with a transceiver and/or control unit installed in the vehicle. The vehicle transceiver and/or control unit is again provided in communication with door locking mechanisms to lock and unlock the vehicle doors in response to lock or unlock signals received from the remote transceiver within some pre-defined range.
In such passive entry systems, however, the remote transceiver carried by an operator is designed to automatically unlock the vehicle as the operator approaches the vehicle, without the need for operation of any switch or pushbutton by the operator. Similarly, the system is further designed to automatically lock the vehicle as the operator, carrying the remote transceiver, moves away from the vehicle.
Exemplary passive entry systems for vehicles are described in U.S. Pat. No. 4,873,530 issued to Takeuchi et al. and entitled “Antenna Device In Automotive Keyless Entry System;” U.S. Pat. No. 4,942,393 issued to Waraksa et al. and entitled “Passive Keyless Entry System;” U.S. Pat. No. 5,499,022 issued to Boschini and entitled “Remote Control System For Locking And Unlocking Doors And Other Openings In A Passenger Space, In Particular In A Motor Vehicle;” U.S. Pat. No. 5,751,073 issued to Ross and entitled “Vehicle Passive Keyless Entry And Passive Engine Starting System;” U.S. Pat. No. 6,049,268 issued to Flick and entitled “Vehicle Remote Control System With Less Intrusive Audible Signals And Associated Methods;” and U.S. Pat. No. 6,236,333 issued to King and entitled “Passive Remote Keyless Entry System.”
However, as is well known to those of ordinary skill in the art, a feature that must be provided in any passive entry system in order for the system to be viable is detecting whether the remote transceiver is inside or outside of the vehicle. In that regard, there are may be several antenna used in a vehicle passive entry system, both inside and outside of the vehicle. The function of the inside antenna is to detect if the remote transceiver is inside the vehicle. It is, however, challenging and costly to prevent electromagnetic fields from the inside antenna from exiting the vehicle, and to prevent electromagnetic fields from the outside antenna from entering the vehicle.
Thus, there exists a need for an improved passive entry system and method that uses inside and outside antenna to detect the location of the remote transceiver. In such a system and method, the remote transceiver would preferably compare the signal strength of signals from the interior and exterior antenna to determine whether the remote transceiver is inside or outside of the vehicle.